#ifndef _PHYSICSBASE_H
#define _PHYSICSBASE_H

#include "Engine.h"
#include "EntityBase.h"

namespace coll2d {
	struct CollisionInfo;
}

/// \todo get rid of this forward declaration somehow
struct vector3d;

namespace Engine {

class Module;
class Events;

class EntityPhysicState;

/** \brief Performs the physical simulation of all Entities
 *
 * This class defines how the physical simulation is performed. Especially how
 * collisions are treated is defined in the function
 * Physics::ResolveCollision() . This function can be modified to simulate
 * dynamics effects such as friction, bouncing, stacking etc..
 *
 * \todo When running along multiple boxes that are perfectly aligned one hangs from time to time at the last box
 */
class PhysicsBase : public Module { 
	public:
		/** \brief Performs the simulation for the next msec milliseconds
		 * \param msec The amount of time that is to be simulated
		 * \param model A pointer to the model that will be used to pass on collision events.*/
		virtual int Simulate (float msec, ModelBase* model = NULL);
		/** \brief Registers the physical state of an Entity */
		virtual void RegisterEntity (EntityPhysicState* entity);
		/** \brief Unregisters the physical state of an Entity */
		virtual void UnregisterEntity (const unsigned int id);
		/** \brief Calculates the next pair of Entities that will collide */
		bool CalcNextCollision (float stepsize,
				unsigned int &reference_entity_id,
				unsigned int &incidence_entity_id,
				coll2d::CollisionInfo &info);

		/** \brief Modes for warping entities when they reach the world boundaries */
		enum WorldWarp {
			WorldWarpModeX = 0,
			WorldWarpModeY,
			WorldWarpModeZ,
			WorldWarpModeLast
		};

		void EnableWorldWarp (WorldWarp mode) {
			mWorldWarp.set(mode, true);
		}
		void DisableWorldWarp (WorldWarp mode) {
			mWorldWarp.set(mode, false);
		}

		/** \brief Sets world boundaries (needed for Entity warping) */
		void SetWorldBounds (const vector3d &min_bound, const vector3d &max_bound) {
			mWorldMin = min_bound;
			mWorldMax = max_bound;
		}

	protected:
		/** \brief Initializes the system */
		virtual int OnInit (int argc, char* argv[]);
		/** \brief Destroys the system (must be called!) */
		virtual void OnDestroy ();

		/** \brief Moves all Entities for delta_msec milliseconds (can be
		 * negative!) */
		void Move (float delta_msec);

		/** \brief Checks whether two given Entities can collide */
		bool CheckPossibleCollisionPair (EntityPhysicState* entity_a, EntityPhysicState* entity_b);
		/** \brief Resolves the collision that CalcNextCollision has found
		 * It resolves a found collision and prevents interpenetration of cached contacts.
		 */
		void ResolveCollision (float stepsize,
				unsigned int reference_entity_id,
				unsigned int incidence_entity_id,
				coll2d::CollisionInfo &info);

		/** \brief Contains all Entities with a physical state */
		std::map<unsigned int, EntityPhysicState*> mEntities;

	private:
		/** \brief Caches the contact information between two entities
		 */
		void ContactCacheAdd (EntityPhysicState* incidence_entity, EntityPhysicState* reference_entity, vector3d normal);
		/** \brief Removes the contact cache information of two entities in contact
		 */
		void ContactCacheRemove (unsigned int entity_a_id, unsigned int entity_b_id);
		/** \brief Checks whether the entries in the contact cache are still valid
		 */
		void CheckContactCache (EntityPhysicState* entity);
		/** \brief Checks whether the entity has to be warped from one world boundary to the other 
		 *
		 * \returns The directions in which the entity should be warped
		 * */
		vector3d CheckEntityWarp (EntityPhysicState* entity, float stepsize);
		/** \brief Performs collision checks for all candidates of warped positions
		 *
		 * \returns >0 for collisions, = 0 for no collisions, < 0 coll2d error
		 */
		int PerformWarpedCollisionChecks (float stepsize,
				EntityPhysicState* entity_a,
				EntityPhysicState* entity_b,
				vector3d warp_directions,
				coll2d::CollisionInfo &info);

		/** \brief Allows to ignore certain kinds of errors reported by coll2d
		 */
		bool HandleColl2dError (int coll2d_result, float stepsize,
		EntityPhysicState* entity_a, EntityPhysicState* entity_b, coll2d::CollisionInfo &info);

		std::bitset<WorldWarpModeLast> mWorldWarp;

		vector3d mWorldMin;
		vector3d mWorldMax;
};

/** \brief Creates an EntityPhysicState with all the required information */
EntityPhysicState* CreateEntityPhysicState (EntityBaseType type, unsigned int id);

}

#endif // _PHYSICSBASE_H